Integrated circuit analysis imaging techniques are frequently used during failure analysis of semiconductor devices. Methods for performing this analysis include collection and analysis of emitted radiation, electron microscopy, and conventional optical imaging. The image derived from the analysis method chosen can be examined to determine several characteristics of the invention, including operational and failure modes of a typical integrated circuit. Though early imaging systems examined only the front surface of the integrated circuit, in recent years it has become common to image the integrated circuit from the backside after performing processing of the backside of the integrated circuit.
Backside imaging allows enhanced viewing of the interconnects, which generally reside on the substrate at the lowest level of the chip. Because the interconnects are a frequent source of failure in an integrated circuit, the ability to clearly view the interconnects greatly reduces the number of defective parts distributed by a manufacturer. It also allows simpler and more accurate failure analysis during the testing phases of product development. Additionally, backside processing provides a clearer view of the components of the integrated circuit as the interconnects do not obscure the view of the electronic components as severely as the components obscure the view of the interconnects in frontside imaging. This again results in more accurate failure and operational analysis.
U.S. Pat. No. 6,107,107, entitled “ANALYZING AN ELECTRONIC CIRCUIT FORMED UPON A FRONTSIDE SURFACE OF A SEMICONDUCTOR SUBSTRATE BY DETECTING RADITATION EXITING A BACKSIDE SURFACE COATED WIH AN ANTIREFLECTIVE MATERIAL,” discloses an imaging system that detects electromagnetic radiation emanating from the backside surface of an integrated circuit. The backside surface is coated with an antireflective coating, a beam of electromagnetic radiation is directed to the backside surface or electrical power is supplied to the circuit, and the radiation emanated from the backside is collected. The emitted radiation is used to analyze the circuit. This method of analysis is not used in the present invention. U.S. Pat. No. 6,107,107 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,168,965, entitled “METHOD FOR MAKING BACKSIDE ILLUMINATED IMAGE SENSOR,” discloses an imaging system that views the backside of an integrated circuit. With this method, the frontside of the circuit is attached to a support substrate and the backside of the circuit is subjected to processing until the semiconductor substrate is removed. A transparent substrate is then attached to the backside of the circuit and an imaging process is performed. The present invention does not operate in this manner. U.S. Pat. No. 6,168,965 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,338,974, entitled “INTEGRATED CIRCUIT ANALYTICAL IMAGING TECHNIQUE EMPLOYING A BACKSIDE SURFACE FILL LAYER,” discloses a method of processing a backside of an integrated circuit to allow analysis of the circuit. With this method, the backside of the circuit is thinned, resulting in a thin semiconductor substrate having peaks and valleys. A fill material is applied to the thin substrate to at least partially fill the valleys. The result is a smother substrate surface. This surface is imaged using any conventional radiation emission imaging technique. The present invention does not use this method for backside imaging. U.S. Pat. No. 6,338,974 is hereby incorporated by reference into the specification of the present invention.
The difficulty in performing failure or operational analysis on an integrated circuit is obtaining a clear view of the components of the circuit. To achieve this, most modern systems attempt to obtain a sufficiently thin and smooth backside surface to allow a clear image to be acquired of the circuit components. This structure is often attained by the addition of structures such as fill materials, transparent substrates, or antireflective coatings. This adds both cost and complexity to an already complex process. Further, these additional components may interfere with the image obtained if they are not applied with absolute precision. The substances may also create undesirable reflections or shadows, thereby distorting the final image. Moreover, the additional elements generally limit the techniques that can be used to image the integrated circuit. It is therefore desirable in the art to have a simple, cost-effective backside imaging process that allows a clear image to be obtained of the components of an integrated circuit by a variety of imaging methods.